On 6/17/2021 6:52 PM, Dave Chinner wrote:

On Thu, Jun 17, 2021 at 10:16:58AM -0500, Alex Sierra wrote:

quoted

From: Ralph Campbell <redacted>

There are several places where ZONE_DEVICE struct pages assume a reference
count == 1 means the page is idle and free. Instead of open coding this,
add a helper function to hide this detail.

v2:
[AS]: rename dax_layout_is_idle_page func to dax_page_unused

Did you even compile test this?

Thanks for catching this Dave, my mistake, I was building without 
CONFIG_FS_DAX, as I was using DEVICE_GENERIC only.
I'll send the corrected patch in replay.

Regards,

Alex Sierra

quoted

Signed-off-by: Ralph Campbell <redacted>
Signed-off-by: Alex Sierra <redacted>
---
  fs/dax.c            |  4 ++--
  fs/ext4/inode.c     |  5 +----
  fs/xfs/xfs_file.c   |  4 +---
  include/linux/dax.h | 10 ++++++++++
  4 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 26d5dcd2d69e..321f4ddc6643 100644
--- a/fs/dax.c
+++ b/fs/dax.c

@@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
  	for_each_mapped_pfn(entry, pfn) {
  		struct page *page = pfn_to_page(pfn);
  
-		WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
+		WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page));

Because you still use dax_layout_is_idle_page() here, not
dax_page_unused()...

quoted

  		WARN_ON_ONCE(page->mapping && page->mapping != mapping);
  		page->mapping = NULL;
  		page->index = 0;

@@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry)
  	for_each_mapped_pfn(entry, pfn) {
  		struct page *page = pfn_to_page(pfn);
  
-		if (page_ref_count(page) > 1)
+		if (!dax_layout_is_idle_page(page))

Here too.

Cheers,

Dave.